This invention relates to a solenoid device applicable to a solenoid switch for an engine starter and, more particularly, to a water cover arrangement particularly suitable for use in a solenoid switch of an vehicular engine starter.
FIG. 1 is a front view illustrating, partially in section, an engine starter to which a conventional electromagnetic attraction device or a solenoid apparatus is mounted. In FIG. 1, the engine starter comprises a front bracket 1, a motor yoke 2, a rear bracket 3 and a solenoid switch 4 mounted to the front bracket 1.
The solenoid switch 4 has a plunger 7 which is movably disposed within an inner passage 6 in the switch case 5 and which is adapted to be electromagnetically attracted by an excitation coil 8. Also, a hook 9 is disposed inside of the plunger 7 and connected to the plunger 7 through a spring 10 and its front end engages with a lever 11. Further, a boot 12 made of rubber is secured at its outer circumference portion to the switch case 5 and secured at its inner circumference portion to a support member 13 placed over the front end portion of the plunger 7 for axially slidably supporting the hook 9. The boot 12 is provided with a vent hole 12a formed in the boot 12 for communicating therethrough the inside and the outside of the boot 12.
The solenoid switch 4 of the above structure is provided with the boot 12 for the water proof and the dust proof of the sliding portions of the plunger 7, thereby to prevent the sliding motion from becoming awkward due to the generation of rust or the like. However, when the end face of the plunger 7 is completely covered by the boot 12, a pressure difference is generated between the inside and the outside of the boot 12, causing an undue deformation in the boot 12 which may result in breaking of the boot 12, so that the vent hole 12a is provided in the boot 12 in order to eliminate the generation of the pressure difference.
The conventional solenoid switch 4 is constructed as above described, and since the boot 12 has the vent hole 12a which is always open, water can enter into the solenoid switch 4 through the vent hole 12a when a large amount of water flies onto the solenoid switch 4. That is, at the occasion of the vehicle running through a pool of water, a large amount of water can enter into the interior of the starter through an opening 1a of the front bracket 1, the water then enters into the interior of the solenoid switch 4 through the vent hole 12a of the boot 12, disadvantageously causing problems of improper operation such as the improper sliding operation of the plunger 7.
Also, while an arrangement as disclosed in Japanese Utility Model Laid-Open No. 60-113940 is proposed, in which an end face of a plunger is covered by a boot and a central portion of the plunger not covered by the boot and a central portion of the plunger not covered by the boot is provided with a through hole for communicating the inside and the outside of the boot, this arrangement also has the same problems as the above-described conventional solenoid switch 4 because the through hole is always kept open.